This invention relates to an optical waveguide probe for observing sample geometry utilizing an atomic force between substances and measuring optical property of a microscopic region of a sample through a probe formed by an optical waveguide, and to a method for manufacturing the same.
At present, in the scanning near field optical microscopes (hereinafter abbreviated as SNOM) measurement is made of sample optical characteristics and geometry by causing a tip-sharpened probe of an optical medium to approach a measurement sample at a distance of less than light wavelength. There is proposed an apparatus, as one of such apparatuses, wherein a linear-formed optical fiber probe vertically held close to a sample at its tip is horizontally vibrated relative to a sample surface, so that a change in amplitude of vibration caused due to shear forces at the sample surface and probe tip is detected by irradiating laser light to the probe tip and detecting a change in a shadow thereof, wherein the sample is moved by a fine movement mechanism to maintain the amplitude constant whereby the spacing between the probe tip and the sample surface is kept constant to detect sample geometry and measure sample light transmission from an intensity of an input signal to the fine movement mechanism.
Also, there is proposed a scanning near field atomic force microscope which uses a hook formed optical fiber probe as a cantilever for the atomic force microscope (hereinafter abbreviated as AFM) to perform AFM actuation, and simultaneously illuminates laser light through an optical fiber probe tip onto a sample to thereby detect sample geometry and measure sample optical properties (No. 174542/1995). FIG. 34 is a structural view showing an optical waveguide probe of a conventional example. This optical waveguide is covered over its periphery by a metal film coating 102. Also, a probe needle portion 103 is sharpened, and the probe needle 103 has an aperture 104 at its tip.
On the other hand, in AFMs utilized as fine region geometrical observing means, utilized broadly are micro-cantilevers of silicon formed by a silicon fabrication process or silicon nitride.
However, there has been a problem in that the optical fiber probe used in a SNOM is manufactured in processes having many steps requiring manual operation with an optical fiber as a material so that mass producibility is low and the shapes such as tip diameter and tip angle are uneven. Also, although high speed scanning control requires an increase in resonant frequency, because the optical fiber itself is used as a cantilever spring material, the spring portion if shortened in order to increase the resonant frequency has an increased spring constant. Also, there has been the problem that the optical fiber is of a thin and long filamentous material and difficult to handle. Also, although the arrangement with a plurality of optical probes enables high speed observation without requiring high speed scanning sweep of a sample surface, the optical fiber probe is manufactured one by one by manual operation and is not suited for a structure having a plurality of probes arranged on the same substrate, i.e., an array form.
On the other hand, the micro-cantilever used in an AFM is high in resonant frequency and high in mass producibility with reduced variation, and possesses the advantages that it is even in mechanical properties such as spring constant and resonant frequency and is easy to handle. However, there has been the problem that it is impossible to conduct light illumination and light detection at the tip portion required in the SNOM.
Also, samples with large steps such as biological samples and polymer samples are considered within the SNOM application scope. However, the micro-cantilever probe needle used in the conventional AFM is as short as approximately 10 microns and it is difficult to measure a sample with large steps. Furthermore, these samples in many cases require measurement in a liquid. However, the AFM micro-cantilever is a cantilever in a plate form and accordingly it is difficult to perform measurement in a liquid.
Therefore, this invention has been made in view of the above, and it is an object to provide an optical waveguide probe which fulfills conditions of excellent mass producibility and eveness, small spring constant, ease of handling, ease of use in a liquid, capability of light illumination and detection, and capability to be arrayed with ease. Also, it is another object to provide a manufacturing method for manufacturing such an optical waveguide probe.
This invention is characterized in that, in an optical waveguide probe having an optical waveguide sharpened at a probe needle portion formed in a hook form and a substrate supporting the optical waveguide, the optical waveguide is characterized in that the optical waveguide is overlaid on the substrate and formed integrally therewith. The optical waveguide formed of a dielectric material is used.
Also, according to the invention, in an optical waveguide probe having an optical waveguide sharpened at a probe needle portion formed in a hook form, a substrate supporting the optical waveguide and a metal film covering the optical waveguide, the optical waveguide characterized in that the optical waveguide is overlaid on the substrate and formed integrally therewith and the probe needle portion of the optical waveguide has at a tip an aperture covered over by the metal film. The optical waveguide is formed of a dielectric. Also, the optical waveguide has a metal film deposited over a dielectric for light transmission.
On the other hand, a method for manufacturing an optical waveguide probe, comprises: a process of forming a mold for embedding the optical waveguide in a substrate, a process of depositing the optical waveguide, a process of separating the optical waveguide along the mold for embedding the optical waveguide, a process of separating the optical waveguide from the substrate.
Of the manufacturing process for an optical waveguide probe, the process of forming a mold for embedding the optical waveguide is any of an isotropic dry etching process or wet etching process using, as etching mask, photo resist having a thickness distribution having been exposed using a photo mask with a gradation, an anisotropic dry etching process using, as an etching mask, photo resist having a thickness distribution exposed using a photo mask with a gradation, an isotropic wet etching or dry etching process utilizing etching undercut to the underneath of an etching mask, a multi-staged anisotropic wet etching process to a silicon substrate using an etching mask formed stepwise with at least two steps, and an anisotropic wet etching process to a silicon substrate.
Also, the process of depositing the optical waveguide in the mold for embedding the optical waveguide is a process of depositing a dielectric material corresponding to the cladding, depositing a dielectric material relatively greater in refractive index than the cladding corresponding to the core, patterning the core, and further depositing a dielectric material corresponding to the cladding. The core patterning is conducted by photolithography using electro-deposition resist.
The process of separating the optical waveguide along the mold for embedding the optical waveguide is a polishing process for depositing a dielectric material in the mold for embedding the optical waveguide, thereafter planarizing by embedding a resin material in a recess formed in a portion of the mold for embedding the optical waveguide, and separating the optical waveguide by polishing to an original substrate surface or deeper than the original substrate surface. Also, the process of patterning the optical waveguide into a probe shape is performed, using electro-deposition resist as etching mask, by an anisotropic dry etching or wet etching process and an isotropic dry etching and wet etching process.
Th process of separating the optical waveguide probe from the substrate is a dry etching process or an anisotropic wet etching process from an opposite surface to a surface formed with the optical waveguide.
According to an optical waveguide probe as described above, it is possible to form the lever portion in a short and thin form as compared to the conventional SNOM optical fiber probe, and to improve the resonant frequency without increasing the spring constant. The optical waveguide portion formed in a hook form, if increased in length, facilitates measurement of a sample having large steps. Also, the rectangular cantilever form stabilizes vibration in a liquid as compared to the conventional AFM cantilever having a flat plate cantilever. Also, light illumination and light detection are possible to an extent that can not be achieved with the convention AFM cantilever.
Also, the use of a silicon process enhances mass producibility, improving shape reproducibility and evenness in mechanical property. Also, because the substrate and the optical wavequide portion are made in one body, handling such as mounting or adjustment is facilitated, similar to the conventional AFM cantilever.
Also, according to the above-described manufacturing method for an optical waveguide probe, the optical waveguide probe is easy to manufacture.
Next, in order to achieve the above object, an optical waveguide probe of this invention comprises a substrate serving as a support member; a columnar optical waveguide formed on the substrate and having one part thereof projecting from the substrate, and being bent toward a sample or a medium and sharpened at a tip; a light reflective layer formed over the optical waveguide except at an aperture at the optical waveguide tip. Also, the optical waveguide is structured by a combination of a cladding and a core.
Also, an optical waveguide probe of this invention comprises a substrate serving as a support member; a columnar optical waveguide formed on the substrate, and being sharpened at a tip on one side as an apex; a light reflective layer formed over the optical waveguide except at an aperture at the optical waveguide tip.
By doing so, similarly to the above, it is possible to form the lever portion in a short and thin form, and to improve the resonant frequency without increasing the spring constant. Also, where the tip of the optical waveguide is bent, it is possible to easily measure a sample having large steps. Further, the columnar shape stabilizes vibration in liquid. Also, light illumination and light detection are possible that can not be made with the conventional AFM cantilever. Also, the use of a silicon process enhances mass producibility, improving shape reproducibility and evenness in mechanical properties.
Also, in the optical waveguide probe of this invention, a groove is formed in a portion of the optical waveguide projecting from the substrate, thereby facilitating bending. Also, a guide groove is provided in the substrate to fix a connecting position of the optical waveguide and the optical fiber, facilitating coupling with an optical fiber.
Next, in manufacturing an optical waveguide probe comprising, a substrate as a support member, a columnar optical waveguide formed on the substrate and having one part thereof projecting from the substrate, and bent toward a sample or a medium and sharpened at a tip, a light reflective layer formed over the optical waveguide except for an aperture at the optical waveguide tip, a method for manufacturing an optical waveguide probe of this invention is characterized in that the bending of the optical waveguide is made by a process of overlaying a material having a different thermal coefficient of expansion from the optical waveguide on one surface of a portion of the optical waveguide projecting from the substrate and heating the material and the optical waveguide. Otherwise, the bending of the optical waveguide is made by a process of forming a substrate for supporting the optical waveguide wherein a material having a different thermal coefficient of expansion from the optical waveguide is overlaid, while heating, on one surface of a portion of the optical waveguide projecting from the substrate.
Also, an optical waveguide is overlaid on a substrate such that one part thereof projects from said substrate, said optical waveguide at a tip is sharpened, and a light reflective layer is formed over said optical waveguide except for a tip to be formed into an aperture, wherein these processes include: a process of forming a material having a different thermal coefficient of expansion from said optical waveguide on one surface of said optical waveguide; and a process of heating said material and said optical waveguide to bend said optical waveguide. Otherwise, these processes include a process of forming while heating, a material having a different thermal coefficient of expansion from the optical waveguide on one surface of the optical waveguide.
In this manner, the use of a material having a different thermal coefficient of expansion from the optical waveguide facilitates the bending of the optical waveguide. This material may be formed over the entire surface of the one surface of the optical waveguide or a surface to be formed into a cantilever.
Also, a method for manufacturing an optical waveguide probe of this invention, characterized in that an optical waveguide is overlaid on a substrate such that one part thereof projects from the substrate, the optical waveguide at a tip is sharpened, and a light reflective layer is formed over the optical waveguide excepting a tip to be formed into an aperture, wherein these processes, wherein these processes include: a process of bending the optical waveguide by heating principally one surface of the optical waveguide.
If the optical waveguide is heated at one surface, it has increased heat absorbing amount than in the opposite surface. Due to this, the one surface is softened so that the optical waveguide is bent by the surface tension. This simplifies the bending process.
Further, in a manufacturing method for an optical waveguide probe of this invention, a groove is provided in the optical waveguide during the above process. The portion provided with the groove is reduced in moment of inertia in section, and facilitated in bending.
A method for manufacturing an optical waveguide probe of this invention, characterized in that a columnar optical waveguide is overlaid on a substrate such that one part thereof projects from the substrate, the optical waveguide at a tip being sharpened, and a light reflective layer being formed over the optical waveguide excepting a tip of the optical waveguide to be formed into an aperture. The columnar shape of the optical waveguide improves the resonant frequency without increasing the spring constant. Further, the columnar shape stabilizes vibration in a liquid. Incidentally, the sharpening for the optical waveguide uses isotropic etching, or anisotropic etching, particularly anisotropic etching in a state the substrate is inclined.
Also, in an optical waveguide probe of this invention, the optical waveguide forming an aperture is formed by three surfaces. Also, it is formed by three surfaces including at least two sets of vertical surfaces. Otherwise, an optical waveguide before the bending process is formed by a generally vertical surface and a generally horizontal surface with respect to a surface of the support substrate contacted with the optical waveguide.
Accordingly, because such a probe aperture of the optical waveguide is formed by an apex of three surfaces including two surfaces with an angle of 90 degrees, where the aperture is placed horizontally close to a sample, the bending amount in the optical waveguide can be reduced thus stabilizing manufacture and desirably improving yield. Also, the decrease in the optical waveguide bending amount reduces the light loss at the bent portion thus improving light transmission efficiency for the optical waveguide.
Also, in an optical waveguide probe of the present invention, a plurality of optical waveguides are arranged on the substrate.
Therefore, it is possible to manufacture an optical waveguide array excellent in evenness with high mass producibility and at low cost,